Hackers penetrated Twitter’s popular TweetDeck feature Wednesday morning, prompting the social networking site to disable the service until it could be fully fixed.

TweetDeck users, who rely on the feature to organize their Twitter feeds, reported seeing pop-up windows with messages such as “Yo!” In addition, hackers were able to send out retweets through some users’ accounts, including @SFGate.

Twitter, based in San Francisco, alerted TweetDeck users around 9:30 a.m. that it had spotted and fixed “a security issue.” The company advised users to log out of TweetDeck, and then log back in to apply the fix. Then, as word circulated online that the patch didn’t appear to work for some users, Twitter reported that it was taking TweetDeck services down to assess the situation.